Empty session_info when rendering with lazy=True

[jyotirmoyjena]

Bug Report

ALL software version info

Python 3.8.10 (tags/v3.8.10:3d8993a, May 3 2021, 11:48:03) [MSC v.1928 64 bit (AMD64)] Panel: 0.13.1 Bokeh: 2.4.3 Param: 1.12.2

Description of expected behavior and the observed behavior

When serving a template with the lazy flag:

pn.panel(main_pane, lazy=True)

The app does not track the session object if started with:

panel serve

But when the admin app is enabled with

panel server --admin

The session_info object is tracked as should be the case. Filing it as a bug, but this could be a design decision, unclear.

Complete, minimal, self-contained example code that reproduces the issue

import panel as pn

input_1 = pn.widgets.Select(options=[1, 2, 3, 4], name='Input 1')
input_2 = pn.widgets.Select(options=[1, 2, 3, 4], name='Input 2')
num_of_calls = 0


def sidebar():
    return pn.Row(pn.Column(pn.Row(input_1), pn.Row(input_2)))


@pn.depends(input_1, input_2)
def main_pane(input1_val, input2_val):
    global num_of_calls
    num_of_calls += 1
    print(pn.state.session_info)
    md = pn.pane.Markdown(f'{input1_val + input2_val} - {num_of_calls}')
    return pn.Row(pn.Column(md))


if __name__.startswith('bokeh'):
    pn.extension()
    t = pn.template.FastGridTemplate(
        site='Panel', title='Test',
        sidebar=sidebar()
    )
    t.main[:1, :2] = pn.panel(main_pane, lazy=True)
    t.servable()

panel server app.py --port 8100

Stack traceback and/or browser JavaScript console output

2022-09-08 18:12:49,924 Bokeh app running at: http://localhost:8100/app 2022-09-08 18:12:49,925 Starting Bokeh server with process id: 11796 {'total': 0, 'live': 0, 'sessions': OrderedDict()} 2022-09-08 18:12:52,338 WebSocket connection opened 2022-09-08 18:12:52,340 ServerConnection created {'total': 0, 'live': 0, 'sessions': OrderedDict()}

With --admin enabled in CLI

panel server app.py --port 8100 --admin

2022-09-08 18:42:52,297 Bokeh app running at: http://localhost:8100/app 2022-09-08 18:42:52,298 Starting Bokeh server with process id: 10332 {'total': 1, 'live': 0, 'sessions': OrderedDict([('07iSav2D2SWW4JkUNvmeOvCQXCaJjINxuCV8D0z9Rqgn', {'launched': 1662642774.96689, 'started': 1662642775.071888, 'rendered': None, 'ended': None, 'user_agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/105.0.0.0 Safari/537.36'})])}

Screenshots or screencasts of the bug in action

[philippjfr]

This is not unexpected, session_info is only tracked when either --admin or --session-history is set. I'd very happily accept suggestions and particularly PRs to clarify this in the documentation.

[jyotirmoyjena]

Thank you for clarifying. I posted it so it can be flagged and fixed if the behavior is unexpected.